The research goals of grant year three are to complete microscopic studies of postmyelographic arachnoiditis and to assess arachnoiditis following intrathecal methylprednisolone. Monkeys will be sacrificed at 1, 2, 4, 7, 14 and 28 days after myelography (Iocarmate or Metrizamide) or a control procedure (lumbar puncture). The arachnoid will be studied by light and electron microscopy. Morphologic changes preceding arachnoid fibrosis will be noted. Monkeys will be injected int rathecally with methylprednisolone acetate (0.15 ml, 40 mg I/ml). Twelve weeks later, animals will be sacrificed. The degree of arachnoiditis will be quantitated by histologic and myelographic techniques and compared with controls (animals injected intrathecally with cerebrospinal fluid).